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<title>Luminance HDR User Manual — Setting up Luminance HDR — External tools</title>
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<h2>External tools</h2>

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<h3>Alignment options</h3>

<p>Luminance HDR can optionally use align_image_stack command line tool bundled with Hugin, a panorama stitcher, for the alignment of slightly misaligned images. When several differently exposed images are taken in the process of creating a High Dynamic Range image, the images are not perfectly aligned, and the quality of the HDR image created will suffer from this. align_image_stack uses the tools available to hugin to optimize the roll, pitch and yaw, as well as some parameters of the lens geometry, to align the images.</p>

<p>align_image_stack doesn't have a lot of relevant options, so we list them here:</p>

<dl>
<dt><b>-a prefix</b></dt>
<dd>Output aligned images as prefix_xxxx.tif</dd>
<dt><b>-e</b></dt>
<dd>Assume input images are full frame fish eye (default: rectilinear)</dd>
<dt><b>-t num</b></dt>
<dd>Remove all control points with an error higher than num pixels (default: 3)</dd>
<dt><b>-f HFOV</b></dt>
<dd>Approximate horizontal field of view of input images, use if EXIF info not complete</dd>
<dt><b>-m</b></dt>
<dd>Optimize field of view for all images, except for first. Useful for aligning focus stacks with slightly different magnification.</dd>
<dt><b>-c num</b></dt>
<dd>Number of control points (per grid) to create between adjacent images (default: 8)</dd>
<dt><b>-l</b></dt>
<dd>Assume linear input files</dd>
<dt><b>-s scale</b></dt>
<dd>Scale down image by 2^scale (default: 1 [2x down-sampling])</dd>
<dt><b>-g gsize</b></dt>
<dd>Break image into a rectangular grid (gsize x gsize) and attempt to find num control points in each section (default: 5 [5x5 grid])</dd>
<dt><b>-v</b></dt>
<dd>Verbose, print progress messages.  Repeat for higher verbosity</dd>
</dl>

<p>By default Luminance HDR just defines the option for verbose printing <tt>-v</tt>. 
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